Great Barrier Reef is the longest reef structure in the world & lies along the continental shelf off Queensland’s east Coast. Great Barrier Reef is 15 million years old in the north & 2 million years old in the south. In1981 Great Barrier Reef was listed as World Heritage Area. It is a unique ecosystem of national & international significance that is under threat from a variety of sources. Great Barrier Reef is clearly visible from space & satellite. The imagery from satellite has helped in understanding the Great Barrier Reef. Great Barrier Reef consists of coral reefs, mangroves & salt flats, rocky reefs, open Ocean and deep sea floor habitats.

Location & Latitude

Great Barrier Reef extends 2300km from Papua New Guinea in the and north of Fraser Island (24 degrees south latitude) in the south. It consists of multiple reefs. Great Barrier Reef world heritage area contains most of the reef extending from Cape York in the north to Lady Elliott Island in the south.

Size

Great Barrier Reef composed of 2900 individual reefs, Reefs range in size from a few thousand sq metres up to 120 sq kilometres. Great Barrier Reef includes 600 Islands. Great Barrier Park Marine Park covers an area of 348 700 sq kilometres.

Shape:

Great Barrier Reef has four regional variations. They are as follows.

Northern Region

In northern region continental shelf is at its narrowest no more then 50 killometers wide. In this region ribbon reefs on the edge of the continental shelf extend to south Cairns. As well, in this region, ribbon reefs are 25 km long & 500metre wide & are separated by channels.In northern region westward of the ribbon reefs the continental shelf has platform reefs & a variety of patch reefs & low wooded isles.

Central Region

In central region continental shelf widens. In central region, scattered patch reefs & crescent reefs that are orientated towards the predominant south.

Mackey region

In Mackey region continental shelf is widest at 300 km. Pompey & Swain are the dominant reefs.

Southern Region

The southern region consists of a chain of 22 reefs. Continental shelf narrows in Southern region.

In southern region many of the reefs are vegetated.

Corals

Corals consist of tiny animals called coral polyps. They have a symbiotic relationship with the microscopic single celled plants. Process waste material from the coral polyp & through photosynthesis produce oxygen & helps the polyp form its calcium carbonate exoskeleton. Coral polyps grow over old corals & build up thick layers over time. Corals feed at night by filtering microscopic zooplankton.

Environmental requirements for optimal coral growth

Corals thrive best in shallow waters between 2 – 30 metres where light is strongest for photosynthesis.

Water temperature of 26 – 27 degrees is needed for the build up of limestone. It must have clear water with low concentrations of inorganic nutrients such as nitrogen & phosphate. If there is no constant high salinity, the corals will die. They need high oxygen levels & coral do best where water is continually oxygenated by wave activity. As well, they require low sediment levels

Coralline algae & sponges:

Sponges & corallines algae excrete silica that helps to cement the reef together. They play a protective role in the ecosystem. Calcium carbonate the excrete coast much of the reef surface

Biodiversity:

Great Barrier Reef has 2000 fish species & 500 coral species.Many of the marine species are endemic

Great Barrier Reef provides nesting ground for endangered & loggerhead turtles. The Rained Island has the world’s largest nesting populations of green turtles & is Australia’s most significant seabird rookery. Great Barrier Reef has the richest faunal biodiversity on the planet. Wonky holes play a significant role in the enrichment of nutrients in the low nutrient ecosystem.

Dynamics of Weather & Climate:

Temperature

The solar energy absorbed by the sea & the movement of ocean currents determine temperature.

Precipitation

Tropical cycles bring torrential rain causing fresh water ponds, which kills corals exposed at low tides.

Floodwaters, which may wash sediments & nutrients out to sea where they may affect, water quality.

Winds

Great Barrier Reef is affected by predominately southeasterly trade winds & periodic summer cyclones.

The shape of individual reefs is in response to dominant winds.

Tropical Cyclones

They consist of intense low-pressure systems. Their impact depends on intensity & location. The cyclones can destroy parts of the reef & move huge blocks of coral onto reef flats. Destroyed coral can take years to rebuild. As well, rain after cyclones can decrease salinity levels causing coral to die.

In addition, cyclones cause patchy disturbance & increase the diversity of the reef as corals recolonise the disturbed area.

Geomorphologic & Hydrological Processes:

Earth Movements

In terms of earth movement four tectonic forces have affected the Great Barrier Reef. They are rifting, continental drift, subsidence & hydroisostasy. 95 million years ago rifting caused the Townsville & Queensland troughs to join close to the edge of the continent. These two deep rift basins determined the shape of the continental shelf & distribution & shape of the reefs. Continental drift influences growth rates of coral. Subsidence has affected Great Barrier Reef twice. Rate of subsidence & the sea level determines reef growth. Hydro – isostasy occurs when the weight of water over the continental shelf causes the land to subside. Great Barrier Reef has undergone many periods of subsidence & release. E.G During the ice ages when the continental shelf was exposed the land rose as the pressure of the water was released.

Weathering

Coral & coralline algae are weathered over time & replaced by younger generations thickening the surface over time.

Erosion

Substratum of the reef consists of calcium carbonate. Coral browsers such as parrotfish erode corals as they browse. Worm species tunnel through coral using acid secretions weakening the structure. Cyclones erode the areas reached by the waves. Low sea levels expose the reef above water & sub aerial erosion processes occur. Over time coral surfaces were eroded by rainwater.

Sediment Formation

Outer reef – sediment consists entirely of broken coral & shell fragments. Browsing fish species erode the reef as the browse creating sediment. Coral polyps constantly replace broken fragments worn away through wave & current action. Myriad organisms recycle sediment & use it as their habitat. Waves & currents wash sediment on the leeward side of structures to form coral cays. If cays are stable enough they are colonised with vegetation & a complete terrestrial ecosystem develops. This is dependent on the surrounding sea. Coral sand holds the reef together. Sediment trapped in holes in the reef is cemented together by coralline algae. 95% of coralline algae are limestone & 5% is living plant tissue. Algal rim of the Great Barrier Reef protects the reef from wave action by causing oncoming waves to collide with backwash.

Transport & Deposition

Water movements in Great Barrier Reef determined by southeasterly winds & currents. 7000 cubic kilometres of water a day is flushed through the system by tides & currents. Currents maintain reef channels & passages. Mixing of waters contributes to the water quality necessary for maintaining the biodiversity of the reef. Wave & tidal currents are responsible for much of the transport & deposition of sediment. Sediment do not escapes the continental slope. Reef structure traps sediment. Some sediment is recycled & cemented together again by coralline algae.

Biogeographical Processes:

Rates of reef growth

Reefs in southern section grow slower then those in the north because of the cooler water temperatures.

Different species are found in different areas of the reef. Slow growing corals use chemical warfare against fast growing corals to maintain their existence. Growth rates of coral found in deep water are slower then those located close to the surface

Resilience

Great Barrier Reef area’s biodiversity & high inertia is resistant to significant change. Coral reef ecosystems have high resistance to cyclonic damage but low resistance to changes in their physical environment requirements. For example only some coral polyp populations are affected by cyclonic storm damage while all populations are affected by increase in sea temperature. Great Barrier Reef low elasticity means it may not fully return to pre stress levels for a long time especially if there is global climatic change.

Coral Spawning

Environmental conditions such as water temperature, light, moon cycle & tidal cycle have to be right or coral spawning will not occur. Coral polyp larvae depend on tides & currents distributing them to favourable colonisation areas. Destroyed areas may be recolonised if environmental conditions are favourable but the process is long term.

Adjustments in response to natural stress

Shape of individual reefs & coral cays is in response to prevailing winds, waves, currents & relict topography. Storm damage creates greater diversity in the reef even though in the short term reefs are damaged.

Impact of sea levels on reefs

Sea levels was stabilised at the present level about 6200 years ago. Reefs grow when sea levels are high & die when they are low. Global warming & tectonic movements causes rises & falls in sea levels. If global warming occurs slowly coral may be able to keep growing to keep pace with rising water levels but if it occurs rapidly then there corals could be destroyed.

Crown of thorns starfish infestations

Crown of thorns starfish is a top coral polyp predator. Outbreaks are natural phenomenon & the starfish is a boom or bust organism. Starfish plays a role in regulating the overgrowth of corals under normal conditions but when its in plague proportions it damages coral reefs severely. Coral takes 12 – 15 years to return to its pre infestation levels.

Reasons for crown of thorns starfish infestations

Crown of thorns starfish infestation occurs because shell collectors remove the starfish’s predator triton shellfish. As well, tropical cyclones trigger favourable breeding conditions. Sediment runoff from coastal areas creates favourable conditions for starfish larvae to survive. In addition overfishing removes predators & upsets the natural food chain & ecosystem balance.

Coral Bleaching

Coral bleaching occurs when water temperature exceeds the tolerance limits for the polyps for a period of weeks. Polyps eject their symbiotic microbes before they die allowing the white limestone exoskeleton to show. Worst case of coral bleaching in Great Barrier Reef occurred in 2002 when 60% of the reef suffered. It’s predicted by 2030 coral bleaching events will occur every year due to global warming.

Fisheries

Great Barrier Reef fishing industry is worth $400 million annually to the local economy & employs many people. Largest harvesting activity in the World Heritage Area & its future needs to be based on ecologically sustainable development. Disruption to food chains is caused through unsustainable overfishing of key species like coral trout. Only 4.6% of GBR is protected from fishing. Prawn trawling is permitted in 50% of the Marine Park & disturbs the sea floor. Populations of the endangered dugong in southern half of the reef have crashed to less then 10% of their original no because of commercial gill netting.

Water Quality & coastal development

Sediment & nutrient runoff to the Great Barrier Reef from terrestrial discharge has increased 4 fold in the past 150 years. River discharges contribute nitrogen & phosphorus to the reef. Reefs prefer low concentrations of these nutrients & die if levels are too high. Presence of these nutrients encourages growth of algae on corals, which kills the polyps. Sewerage effluent from coastal towns & resorts on the reef has damaged the reef & introduces the risk of pathogens. Green Island pumped sewerage into the ocean, which has caused the est. of sea grass beds at the expense of hard corals.

Shipping & Oil Spills:

Shipping accidents are a concern. Shipping routes pass through the Great Barrier Reef & there have been 2 groundlings of large container vessels over the past few years due to negligence. Antifouling agent in the paint on hulls of ships is toxic.

Tourism & Recreation:

In terms of tourism 2.4 million people visit Great Barrier Reef each year. Economic value of tourism to the Great Barrier Reef is $1.5 billion per year. Tourists trample the reef & remove corals & shells. Sewerage from resorts that is pumped into the reef damaging corals & encouraging growth of algae & sea grasses. Recreational fishing can lead to over fishing on these reefs that are close to the shore & frequently visited. Controversial road near Cape Tribulation causes sediment runoff, which blankets & kills unique fringing reefs in the area.

Reasons for Protecting the Great Barrier Reef

Great Barrier Reef is of intrinsic value as its one of the most beautiful ecosystems on earth. Great Barrier Reef is has economic value for Australia. Great Barrier Reef is an important reservoir for biological diversity as it contains many undiscovered species. It is the World’s largest reef ecosystem and its protection is vital because it is a recognized natural wonder of the world. Great Barrier Reef plays important role in global carbon cycle. As well it is important to protect Great Barrier Reef because it prevents coastal erosion.

Traditional Management

About forty Aboriginal and Torres Strait Islander tribal groups have territories adjacent to the reef. The traditional management was centred on stewardship, which involves looking after the environment and preserving it for future generations. Small population levels and low level of technology do not place stress on the ecosystems. The traditional management strategies are effective because of low technology and small population.

Aboriginal and Torres Strait Islanders sustain fisheries by a system of taboos and traditions that were based on religion & legend. Long-term management strategies of Indigenous involve restriction on species caught, closed seasons, taboos, designated areas for individuals/groups and sustainable methods of hunting.

Above all, indigenous management was underpinned by an understanding of the resource base. It was generally regarded as effective with few negative outcomes in an environmental protection point of view.

Contemporary Management

Contemporary management practice of Great Barrier Reef is based on the multiple use of the area. Great Barrier Reef was established world’s largest marine park in 1975 and became world heritage area listed in 1981. The contemporary management included extensive scientific research into all aspects of coral reefs from the biology to the ecology. The Great Barrier Reef Marine Park authority is primarily responsible for the area. They have used three main strategies, which are a 25-year strategic plan, marine park zoning and plans of management.

The 25-year strategic plan

The 25-year strategic plan was developed in 1994. The basis of this plan is to ensure the wise use of the area for the future. This plan was endorsed by 70 organisations. As well, this plan identified broad strategy areas such as Conservation, resource management, education, research, and recognition of Aboriginal and Torres Strait Islands interests. For each of these broad areas the plan provides the rationale, 25 – year objectives, 5-year objectives and strategies to fulfill these objectives.

Marine park zoning

Marine park zoning is the primary management tool that provides strategic framework for management.

This zoning activity separates activities that may conflict with each other and protects sensitive areas.

This Zoning provided for the replenishment of areas and seasonal closures. In the Marine Park75% is zoned for general use allowing shipping & trawling. Less then 3% is zone as national park or preservation. Mining and oil drilling is prohibited in these marine zones.

Plans of management

Aim to ensure the appropriate proposals are developed to reduce or eliminate threats to nature and conservation values. The other aim ensures activities within the Marine Park are managed on the basis of ecologically sustainable use. Queensland Parkes and Wildlife Service are responsible for the day-to-day management of the Great Barrier Reef. Officers manage the Great Barrier Reef through resource protection programs, visitor education services and park monitoring and surveillance programs.